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Abstract:

Near-infrared spectra were measured for water-methanol mixtures with a methanol content of 0-100 wt % at 25 °C. The second derivative of the NIR spectra clearly reveals that the first overtones of the
CH3 asymmetric stretching modes of methanol near 5950 and 5900 cm-1 show a downward shift by about 30 cm-1 with the increase in the concentration of methanol. This is unambiguous
evidence for the direct interaction of the CH3 group of methanol with the OH group of water. Similar downward shifts were also observed for water-ethanol and water-1-propanol mixtures, although
the shifts are much smaller for the water-ethanol and water-1-propanol mixtures. Based upon the results of NIR spectra, we propose a model for the interaction between the C-H bond of the CH3
group of methanol and water. This intermolecular interaction is analogous to the intramolecular "(O) CH · · · O" interaction in compounds having both a CH3 group binding
to an oxygen atom and an OH group. This paper demonstrates novel potential of NIR spectroscopy in investigating interactions containing a C-H bond.

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